Many drugs are administered in racemic form and others undergo metabolism to form chiral metabolites. The chiral nature of most biologically important molecules inevitably results in differences between drug enantiomers in transport, binding and metabolism--hence differences in biological activity. Establishing a relationship between pharmacological activity, toxicology and steroselectivity of metabolic processes may lead to the production of new and better drugs and to better use of present drugs. Quantitation of the individual enantiomers in biological systems is of importance in studying the stereochemical differences, but is extremely difficult due to the inherent similarity of enantiomers. Our hypothesis is that stereoselective antibodies can be obtained and utilized in radioimmunoassay (RIA) procedures for the determination of one enantiomer in the presence of the other. This is supported by certain basic data in the literature and preliminary work in our laboratory. We propose to synthesize optically pure haptens based on drug molecules (initially warfarin and pentobarbital), conjugate them to protein and use the conjugates to induce antibody formation in animals. Optically pure drug enantiomers will be radiolabeled and used in conjunction with the antibodies to develop stereoselective RIA's. The applicability of these will be tested in animal systems. Drug interaction effects as well as effects of age, sex, and disease on enantiomer metabolism may be of clinical significance. We believe the proposed methodology will greatly assist in investigating such problems.